| 1. |
- Alfredsson, Bo, et al.
(författare)
-
Initiation and Growth of Standing Contact Fatigue Cracks
- 2000
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 65:1, s. 89-106
-
Tidskriftsartikel (refereegranskat)abstract
- In the standing contact fatigue test an indenter subjects a case hardened test specimen to a stationary but pulsating contact load. Two crack types appearing in the test specimen are investigated. The ring/cone cracks are surface cracks that circumvent the contact area, whereas the lateral cracks are horizontal sub-surface cracks. The initial crack lengths are determined for both crack types. Actual crack paths from experiments are evaluated numerically. For each crack tip position, stress intensity factors are determined from J(1) and J(2) integrals. The stress intensity ranges are compared to criteria for fatigue crack propagation rate and direction. As the cracks propagate, they orient in the direction with mode II loading close to zero.
|
|
| 2. |
- Bjerkén, Christina, PhD, 1962-, et al.
(författare)
-
A numerical method for calculating stress intensity factors for interface cracks in bimaterials
- 2001
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 68:2, s. 235-246
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a method For obtaining the complex stress intensity factor (or alternatively the corresponding energy release rate and mode mixity) for an interface crack in a bimaterial using a minimum number of computations. A crack closure integral method for homogeneous materials developed by Rybicki and Kanninen has been modified to include mismatch in material properties. This was achieved directly from the nodal forces at the crack tip and the displacements near the tip as obtained from a finite element analysis using only four-node constant strain elements. Numerical calculations for tensile and mixed mode loading showed good agreement with results from corresponding analytical solutions. The main advantages of this method are that it is straightforward and easy to use and that the number of calculations needed to obtain the stress intensity Factors can be held to a minimum. (C) 2000 Elsevier Science Ltd. All rights reserved.
|
|
| 3. |
|
|
| 4. |
- Faleskog, Jonas, et al.
(författare)
-
A probabilistic model for cleavage fracture with a length scale - parameter estimation and predictions of stationary crack experiments
- 2004
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 71:1, s. 57-79
-
Tidskriftsartikel (refereegranskat)abstract
- This study presents a large experimental investigation in the transition temperature region on a modified A508 steel. Tests were carried out on single-edge-notch-bend specimens with three different crack depth over specimen width ratios to capture the strong constraint effect on fracture toughness. Three test temperatures were considered, covering a range of 85 degreesC. All specimens failed by cleavage fracture prior to ductile tearing. A recently proposed probabilistic model for the cumulative failure by cleavage was applied to the comprehensive sets of experimental data. This modified weakest link model incorporates a length scale, which together with a threshold stress reduce the scatter in predicted toughness distributions as well as introduces a fracture toughness threshold value. Model parameters were estimated by a robust procedure, which is crucial in applications of probabilistic models to real structures. The conformity between predicted and experimental toughness distributions, respectively, were notable at all the test temperatures.
|
|
| 5. |
- Jernkvist, Lars-Olof
(författare)
-
Fracture of wood under mixed mode loading : II. Experimental investigation of Picea abies
- 2001
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 68:5, s. 565-576
-
Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation of mixed mode I/II fracture in Norway spruce (Picea abies) is presented. Mixed mode fracture is studied in two principal crack systems, RL and LR, in which the crack planes extend along and across the wood fibres, respectively. The investigation shows that onset of mixed mode cracking can be predicted with a very simple fracture criterion in both these crack systems. However, the applicability of the fracture criterion to cross-fibre cracks is limited to configurations, in which the crack tip T-stress, i.e. the non-singular stress acting parallel to the crack plane, is low.
|
|
| 6. |
- Jernkvist, Lars-Olof
(författare)
-
Fracture of wood under mixed mode loading : I. Derivation of fracture criteria
- 2001
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 68:5, s. 549-563
-
Tidskriftsartikel (refereegranskat)abstract
- A mixed mode I/II fracture criterion applicable to cracks oriented both along and across the fibres in wood is derived within the framework of linear elastic fracture mechanics. The use of a common fracture criterion for both types of cracks is made possible by the fact that cracks in wood generally propagate along the fibres, irrespective of both the original crack orientation and the degree of mode mixity. The derived criterion is simple, and contains a single material dependent fracture parameter. The applicability of the fracture criterion to spruce (Picea abies) is experimentally validated in part two of the paper
|
|
| 7. |
- Jivkov, Andrey
(författare)
-
Fatigue corrosion crack extension across the interface of an elastic bi-materia
- 2004
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 71:7, s. 1139-1153
-
Tidskriftsartikel (refereegranskat)abstract
- In this work crack propagation in a bi-material composed of a thin elastic layer ideally bonded to a large elastic substrate is studied. A flaw is assumed existing on the surface of the layer. Cracks nucleate from the flaw and propagate through the bi-material. The cracks have realistic geometrical shapes, where the crack tip is an integral part of the crack surface. Thus the crack propagation is associated with a crack surface evolution. Material loss due to corrosion of the crack surface is the physical ground for the evolution. A controlling mechanism for the surface advancement is the rupture of a brittle corrosion-protective film, which is continually building-up along the corroding surface. The rate of surface evolution is a function of the degree of protective film damage, caused by the surface straining. This leads to a moving boundary formulation, for which a numerical solution is proposed. Fatigue loading is considered as a suitable way to maintain crack evolution at a constant peak load level. Under the assumed model, the cracks always pass the interface. The elastic mismatch is shown to influence the growth rate variation around the interface. Crack extensions are presented as functions of the elastic mismatch and as functions of the initial flaw size. It is shown how the results can be used in designing bi-material systems. A typical morphology evolution of a crack passing through an interface with a weak-stiff transition is presented. An example of fatigue corrosion fracture is offered, which shows that the crack morphology of the model resembles the one observed in reality. It is concluded that the realistic crack geometry is an effective concept and the moving boundary formulation could be a very successful tool for simulating realistic crack propagation.
|
|
| 8. |
- Jivkov, Andrey, et al.
(författare)
-
Strain-driven corrosion crack growth : A pilot study of intergranular stress corrosion cracking
- 2002
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 69:18, s. 2095-2111
-
Tidskriftsartikel (refereegranskat)abstract
- This work proposes a model for corrosion driven crack growth. The model poses a moving boundary problem, where a chemical attack removes material from the body. The rate of the chemical attack is a function of the strain along the body surface. No crack growth criterion is needed for the analysis. A finite strain formulation is used and the material model is assumed hyperelastic. The problem is stated for a large body, containing a large crack. A low frequency cyclic loading is considered. Thus, corrosion is assumed to dissolve material with a rate approximately proportional to the strain rate. The problem is solved using finite element method based program, enhanced with a procedure handling the moving boundary. Parametric studies are performed for a series of different initial shapes of the near-tip region. Presented results show that the crack growth rate is largely dependent on the initial crack geometry. For a set of initial shapes and load levels steady-state conditions of growth are achieved, while for the others the cracks show tendency to branch.
|
|
| 9. |
- Lorentzon, M., et al.
(författare)
-
A path independent integral for the crack extension force of the circular arc crack
- 2000
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 66:5, s. 423-429
-
Tidskriftsartikel (refereegranskat)abstract
- A path independent integral expression for the crack extension force of a two-dimensional circular arc crack is presented. The integral expression, which consists of a contour and an area integral, is derived from the principle of virtual work. It is implemented into a FEM post-processing program and the crack extension force is calculated for a circular are crack in a linear elastic material. Comparison with exact solutions by Cotterell and Rice for the effective elastic stress intensity factor shows acceptable accuracy for the numerical procedure used
|
|
| 10. |
- MackAldener, M., et al.
(författare)
-
Analysis of crack propagation during tooth interior fatigue fracture
- 2002
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 69:18, s. 2147-2162
-
Tidskriftsartikel (refereegranskat)abstract
- Tooth interior fatigue fracture is a failure mode that is initiated as a fatigue crack in the interior of the tooth of a gear. TIFF cracks have been observed in case hardened idler gears. A fracture mechanical analysis of a TIFF crack is performed utilising FEA. A 3D TIFF crack is modelled at a position in the tooth that corresponds with an observed crack surface. The different material properties in the case and the core, determined by mechanical testing, are considered, as well as the residual state of stress due to case hardening. Various crack lengths are analysed to estimate crack propagation both into the core and into the case. The following results have been found: A TIFF crack initiated slightly under the case layer will propagate into the case layer where it stops. . The main crack propagation will take place in the core. . The crack propagation is only a small portion of the total life (order of 10(5) cycles). . After reaching the case layer the TIFF crack eventually deflects toward the tooth root and the upper part of the tooth falls off. The crack deflection is due to redistribution of contact loading. Several gear teeth pairs are simultaneously in contact and the cracked tooth is loaded less than the uncracked during this stage of life.
|
|
| 11. |
- Månsson, Tomas, et al.
(författare)
-
Closure effects on fatigue crack growth rates at constant and variable amplitude loading
- 2004
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 71:10-sep, s. 1273-1288
-
Tidskriftsartikel (refereegranskat)abstract
- Accurate measurements of fatigue propagation rates after single and during repetitive overloads were performed. It was shown that plastic deformations in the crack tip region and in the crack wake cause crack closure that is of major importance for crack growth rates. The consequences of this for methods to determine certain material properties are discussed. An improved method to measure closure free propagation rate data was utilised. The possibilities and shortcomings of compliance methods to determine crack closure levels are pointed out. The relevance of using DeltaK(I,eff) = K-I,K-max - K-I,K-lim, where K-I,K-lim possibly could be interpreted as the crack closure level was investigated and is discussed. A method to predict average crack propagation rates at block loadings consisting of well-defined load cycles of different amplitudes and R-factors was suggested. Three-dimensional effects after overloads were observed. These observations confirmed that the crack closure behaviour also depends on geometry of the specimen.
|
|
| 12. |
- Nilsson, Fred L., et al.
(författare)
-
Growth of surface cracks under constant and variable amplitude loading
- 2004
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 71:12, s. 1725-1735
-
Tidskriftsartikel (refereegranskat)abstract
- Fatigue crack growth experiments were performed on surface cracked tensile specimens of Inconel 718 at 400 degreesC. The loading was carried out at constant as well as at variable amplitude. The experimental results for the mean growth rate were compared with predictions based on data obtained from testing of compact tension specimens. Both nominal data as well as data corrected from measured crack closure were used in the predictions. The corrected data provided much better predictions than the nominal ones indicating that the level of crack closure during the testing of the surface cracked specimens was much lower than in compact tension specimens.
|
|
| 13. |
- Ribeiro-Ayeh, Steven, et al.
(författare)
-
Strength prediction of beams with bi-material butt-joints
- 2003
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 70:12, s. 1491-1507
-
Tidskriftsartikel (refereegranskat)abstract
- Failure of bi-material interfaces is studied with the aim to quantify the influence of the induced stress concentrations on the strength of the interfaces. The suggested approach is applied to a specimen configuration where two different materials are butt-joined to form a two-material beam. Strength predictions for different interface bias are made and verified in experiments where a polymer foam material is joined with members of either aluminium or Plexiglas.The predictions are made using a simple point-stress criterion in combination with highly accurate finite element calculations. The point-stress criterion was known from earlier work to give accurate predictions of failure at cracks and notches but had to be slightly modified to become applicable for the studied configurations. Both the strength and the cross-over from local, joint-induced failure to global failure were predicted with reasonable accuracy.
|
|
| 14. |
- Schon, J., et al.
(författare)
-
Numerical and experimental investigation of a composite ENF-specimen
- 2000
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 65:4, s. 405-433
-
Tidskriftsartikel (refereegranskat)abstract
- An extensive numerical and experimental investigation has been carried out regarding fracture mechanical properties for the end notch flexure (ENF) specimens. Static and cyclic properties were studied for different interfaces and for several graphite/epoxy composites. State of the art numerical analyses are described and experimental results are interpreted in terms of usefulness for applications to real structures. The FEM results were compared with beam models and it was found that for the specimen with a zero interface the beam models were acceptable whereas for the specimens with non-zero interface they did show a large error. Numerically, it was found that the effect of friction lowers the energy release rate by a few percent. Experimental results showed that for specimens with non-zero interfaces the delamination crack changed interface. (C) 2000 Elsevier Science Ltd. All rights reserved.
|
|
| 15. |
- Varias, A.G., et al.
(författare)
-
Temperature and constraint effects on hydride fracture in zirconium alloys
- 2000
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 65:1, s. 29-54
-
Tidskriftsartikel (refereegranskat)abstract
- The fracture of hydrides in zirconium alloys is under consideration. According to the present boundary value problem, a hydride platelet lies ahead of a semi-infinite crack, along the crack plane. The surrounding material is elastic-plastic zirconium alloy. The platelet is either continuous or split into two parts, connected by a ductile matrix ligament. At distances from the crack tip, which are large compared to the hydride and the plastic zone size, the K-T field is applied and mode I, plane strain and contained yielding conditions prevail. Hydride platelet failure initiation and growth is simulated by using a de-cohesion crack growth model and the stress intensity factor, which causes fracture, is estimated at various temperatures as well as under various constraint conditions. Comparison of the calculated temperature effect on toughness with the experimental one is satisfactory. Fracture toughness decreases with T-stress. This effect is attributed to the interaction of the K-T field with hydride expansion, during precipitation. The reduction becomes more important at elevated temperatures and moderates the benefits on fracture toughness, caused by temperature increase. In addition to the detailed finite element results, analytical estimates on fracture toughness are presented, based on a cohesive zone model
|
|
| 16. |
- Andersons, Janis, et al.
(författare)
-
Statistical model of the transverse ply cracking in cross-ply laminates by strength and fracture toughness based failure criteria
- 2008
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 75:9, s. 2651-2665
-
Tidskriftsartikel (refereegranskat)abstract
- Cross-ply laminate subjected to tensile loading provides a relatively well understood and widely used model system for studying progressive cracking of the transverse ply. This test allows to identify material strength and/or toughness characteristics as well as to establish relation between damage level and the composite stiffness reduction. The transverse ply cracking is an inherently stochastic process due to the random variability of local material properties of the plies. The variability affects both crack initiation (governed by the local strength) and propagation (governed by the local fracture toughness). The primary aim of the present study is elucidation of the relative importance of these phenomena in the fragmentation process at different transverse and longitudinal ply thickness ratios. The effect of the random crack distribution on the mechanical properties reduction of the laminate is also considered. Transverse ply cracking in glass fiber/epoxy cross-ply laminates of the lay-ups [02/902]s, [0/902]s, and [0/904]s is studied. Several specimens of each lay-up were subjected to uniaxial quasistatic tension to obtain crack density as a function of applied strain. Crack spacing distributions at the edge of the specimen also were determined at a predefined applied strain. Statistical model of the cracking process is derived, calibrated using crack density vs. strain data, and verified against the measured crack spacing distributions.
|
|
| 17. |
- Biel, Anders, et al.
(författare)
-
Effects of constitutive parameters on the accuracy of measured fracture energy using the DCB-specimen
- 2008
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 75:10, s. 2968-2983
-
Tidskriftsartikel (refereegranskat)abstract
- Several methods exist to estimate the fracture energy for adhesive joints using the double cantilever beam specimen and linear elastic fracture mechanics. Since the mechanical properties of all adhesives are non-linear, errors are generated. By use of an exact solution experiments are simulated. These are evaluated with eight different methods. The influence of the constitutive parameters is systematically studied. This influence is small for most methods. The error due to the choice of evaluation method is considerably larger. One of the commonly used methods gives accurate results; the error is less than 3%. However, most methods yield substantial errors.
|
|
| 18. |
- Birgisson, Björn, et al.
(författare)
-
Determination and prediction of crack patterns in hot mix asphalt (HMA) mixtures
- 2008
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 75:3-4, s. 664-673
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a comparison between predicted and measured crack patterns developing in hot mix asphalt (HMA) mixtures during common fracture tests. A digital image correlation (DIC) System was applied to obtain displacement/strain fields and for detecting crack patterns. The resulting cracking behavior was predicted using a displacement discontinuity boundary element method to explicitly model the microstructure of HMA. The predicted fracture initiation and crack propagation patterns are consistent with observed cracking behavior. The results imply that fracture in mixtures can be modeled effectively using a micro-mechanical approach and that crack propagation patterns can be captured using the DIC System.
|
|
| 19. |
- Bjerkén, Christina, et al.
(författare)
-
A study of the influence of grain boundaries on short crack growth during varying load using a dislocation technique
- 2004
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 1873-7315 .- 0013-7944. ; 71:15, s. 2215-2227
-
Tidskriftsartikel (refereegranskat)abstract
- The propagation of short cracks in the neighbourhood of grain boundaries have been investigated using a technique were the crack is modelled by distributed dislocation dipoles and the plastic deformation is represented by discrete dislocations. Discrete dislocations are emitted from the crack tip as the crack grows. Dislocations can also nucleate at the grain boundaries. The influence on crack growth characteristics of the distance between the initial crack tip and the grain boundary has been studied. It was found that crack growth rate is strongly correlated to the dislocation pile-ups at the grain boundaries. (C) 2004 Elsevier Ltd. All rights reserved.
|
|
| 20. |
- Bjerkén, Christina, et al.
(författare)
-
Simulation of corrosion fatigue crack growth under mixed-mode loading
- 2008
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 1873-7315 .- 0013-7944. ; 75:3-4, s. 440-451
-
Tidskriftsartikel (refereegranskat)abstract
- The kinking of a corrosion crack due to mixed-mode fatigue loading is studied using an adaptive finite element procedure. The rate of material dissolution is assumed to be proportional to the stretching of the corroding surface. The dissolution of material is governed by a corrosion law, where no criterion is needed for neither crack growth nor growth direction. The problem is treated as a general moving boundary problem. The kink angles are found to be in very good agreement with results for sharp cracks using criteria reported in the literature.
|
|
| 21. |
- Bremberg, Daniel, et al.
(författare)
-
Automatic crack-insertion for arbitrary crack growth
- 2008
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 75:3-4, s. 404-416
-
Tidskriftsartikel (refereegranskat)abstract
- A crack-insertion tool for automatic non-planar crack propagation calculations is under development. The final volume mesh of the cracked structure is achieved by a new approach. The cracked structure boundary is modelled as a discretized skin. A tube-like domain enclosing the crack-front is traced and filled with hexahedral elements while the remaining cracked structure is meshed with tetrahedral elements. The two separate meshes are finally connected by linear MPC equations. Results show that the method works very well for curved crack shapes in complex structures.
|
|
| 22. |
- Cadario, Alessandro, et al.
(författare)
-
Fatigue growth of short cracks in Ti-17 : experiments and simulations
- 2007
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 74:15, s. 2293-2310
-
Tidskriftsartikel (refereegranskat)abstract
- The fatigue behaviour of through thickness short cracks was investigated in Ti-17. Experiments were performed on a symmetric four-point bend set-up. An initial through thickness crack was produced by cyclic compressive load on a sharp notch. The notch and part of the crack were removed leaving an approximately 50 mu m short crack. The short crack was subjected to fatigue loading in tension. The experiments were conducted in load control with constant force amplitude and mean values. Fatigue growth of the short cracks was monitored with direct current potential drop measurements. Fatigue growth continued at constant R-ratio into the long crack regime. It was found that linear elastic fracture mechanics (LEFM) was applicable if closure-free long crack growth data from constant K-1max test were used. Then, the standard Paris' relation provided an upper bound for the growth rates of both short and long crack.The short crack experiments were numerically reproduced in two ways by finite element computations. The first analysis type comprised all three phases of the experimental procedure: precracking, notch removal and fatigue growth. The second analysis type only reproduced the growth of short cracks during fatigue loading in tension. In both cases the material model was elastic-plastic with combined isotropic and kinematic hardening. The agreement between crack tip opening displacement range, cyclic J-integral and cyclic plastic zone at the crack tip with Delta K-1 verified that LEFM could be extended to the present short cracks in Ti-17. Also, the crack size limits described in the literature for LEFM with regards to plastic zone size hold for the present short cracks and cyclic softening material.
|
|
| 23. |
- Cadario, Alessandro, et al.
(författare)
-
Fretting fatigue crack growth for a spherical indenter with constant and cyclic bulk load
- 2005
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 72:11, s. 1664-1690
-
Tidskriftsartikel (refereegranskat)abstract
- Fatigue growth of edge cracks subjected to non-proportional fretting loads was investigated experimentally and numerically. The cracks were produced during fretting experiments with a spherical contact between two alpha + beta titanium alloys. Constant normal load was combined with cyclic tangential load and constant or cyclic bulk load. Crack propagation was detected during the experiments by strain gauges on the specimen surface and acoustic emission measurements. A parametric crack growth description procedure was used to model fatigue growth of the three-dimensional fretting cracks that were loaded with multiaxial and non-proportional stresses from the fretting contact. The predicted crack growth lives and crack shapes agreed with the experimental results. A crack path prediction based on the maximum principal value of the stress range tensor Delta sigma(ij) was evaluated.
|
|
| 24. |
- Carlberger, Thomas, et al.
(författare)
-
An explicit FE-model of impact fracture in an adhesive joint
- 2007
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 74:14, s. 2247-2262
-
Tidskriftsartikel (refereegranskat)abstract
- Dynamic fracture of an adhesive layer in a structure is analysed. The structure represents some specific properties of an automotive structure and is simple enough to allow for closed form solutions obtained by the method of characteristics. These solutions are compared to results of explicit FE-analyses. The FE-solutions agree with the closed form solutions. Damage is included in the FE-model. Three constitutive models of the adhesive layer are used. It is shown that an amplification of the strain rate is achieved in the adhesive layer. It is also shown that an artificially increased flexibility of the adhesive in an aluminium structure gives only minor influences of the general behaviour. In some load cases, the adhesive layer will experience repeated loading/unloading. It is shown that in these cases an explicit FE-analysis with a “large” time step is more prone to give immediate rupture. Thus, the method is conservative.
|
|
| 25. |
- Chowdhury, K.A., et al.
(författare)
-
An analysis of impact-induced deformation and fracture modes in amorphous glassy polymers
- 2008
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 75:11, s. 3328-3342
-
Tidskriftsartikel (refereegranskat)abstract
- The finite deformation response of a planar block of polymer material subject to impact loading is analyzed using two constitutive models for glassy polymers, a reference Drucker-Prager type model and a physics-based macromolecular model, supplemented by a phenomenological model for craze initiation and widening. Full transient finite element analyses are carried out using a Lagrangian formulation of the field equations. The analyses allow an assessment of possible failure mechanisms under dynamic loading and the ability of the different models to predict such behavior. The results highlight the effect of the stress-strain behavior of polymers, notably the post-yield softening and large strain hardening, on localization of plastic flow. This behavior is adequately captured only by the macromolecular model.
|
|
| 26. |
- Dahlin, Peter, et al.
(författare)
-
Mode I fatigue crack growth reduction mechanisms after a single mode II load cycle
- 2006
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 73:13, s. 1833-1848
-
Tidskriftsartikel (refereegranskat)abstract
- A single Mode 11 load cycle, large enough to create residual displacements, decreases the subsequent Mode I crack growth rate. The distance for Mode I crack growth rate to fully recover, i.e., revert to the same da/dN as before Mode 11 load, is much longer than Mode 11 plastic zone size. The higher Mode 11 load, the larger is the reduction in growth rate and the longer the recovery distance. Higher Mode I R-ratio means smaller reduction in growth rate. Above a certain R-ratio, no reduction occurs at all. In the present study it is found that the reduction in growth rate is solely caused by crack closure due to tangential displacement of crack-surface irregularities that induce a surface mismatch between the upper and lower crack faces. The mechanism is called Mode II-induced crack closure. A model based on both analytical and experimental results is developed in order to estimate the degree of Mode II-induced crack closure after a Mode 11 load.
|
|
| 27. |
- Hansson, Per, et al.
(författare)
-
Computationally efficient modelling of short fatigue crack growth using dislocation formulations
- 2008
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 1873-7315 .- 0013-7944. ; 75:10, s. 3189-3205
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedIn an attempt to develop it computationally efficient model for simulation of fatigue crack growth of microstructurally short cracks two dislocation based models have been compared. In both models, the geometry of the boundary and the crack is described using dislocation dipole elements, whereas the plasticity is described either by discrete dislocations or by distributed dipole elements. The two models were found to agree qualitatively its well as quantitatively. It was concluded that modelling the plasticity by dipole elements becomes comparatively increasingly more time efficient with increasing grain size plastic zone size. However, plasticity modelling by dipole elements showed to provide somewhat higher crack growth rates.
|
|
| 28. |
|
|
| 29. |
- Hägglund, R., et al.
(författare)
-
Influence of damage in the vicinity of a crack-tip in embossed low-basis-weight paper
- 2007
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 74:11, s. 1758-1769
-
Tidskriftsartikel (refereegranskat)abstract
- It is experimentally observed that the fracture process developed in an embossed paper sample having a periodic matrix organized pattern is distributed over several indentation rows in the region near a macroscopic crack. This observation suggests that the stresses at the tip of the crack is shielded by damage in neighboring rows of indentation: energy dissipation may occur not only at the tip of the main crack, but in several indentation rows parallel to the main crack. In this investigation, a model describing the in-plane fracture behavior of embossed low-basis-weight paper is developed. It is found that the model is capable of capturing the development of damage in rows parallel to the main crack and compares well with experimental results.
|
|
| 30. |
- Högberg, J. Li, et al.
(författare)
-
Specimen proposals for mixed mode testing of adhesive layer
- 2006
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 73:16, s. 2541-2556
-
Tidskriftsartikel (refereegranskat)abstract
- The experimental methods to determine the fracture properties for adhesives under mixed mode loading is not as well established as compared to such methods for adhesives under pure mode loading. Some controversies exist regarding the decomposition of the mode mixity. For a flexible linear elastic adhesive, the mode mixity of a single-layer adhesive joint is directly related to the deformation of the adhesive layer at the crack tip. The governing equations for linear elastic single-layer adhesive joints show that the mode mixity depends on the external loads, the properties of the adherends and often on the flexibility of the adhesive layer. This implies some fundamental problems that have to be addressed before an experimental method can be established. The purpose of this paper is to investigate different specimen configurations for mixed mode loading. Requirements for the design of a specimen configuration are given. A new specimen configuration is proposed based on the geometry of a semi-infinite symmetric DCB-specimen. According to this study, the proposed test specimen offers exceptional flexibility, variety and stability.
|
|
| 31. |
|
|
| 32. |
|
|
| 33. |
|
|
| 34. |
- Kroon, Martin, et al.
(författare)
-
A probabilistic model for cleavage fracture with a length scale - Parameter estimation and predictions of growing crack experiments
- 2008
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 75:8, s. 2398-2417
-
Tidskriftsartikel (refereegranskat)abstract
- A probabilistic model for the cumulative probability of failure by cleavage fracture was applied to experimental results where cleavage fracture was preceded by ductile crack growth. The model, introduced by Kroon and Faleskog [Kroon M, Faleskog J. A probabilistic model for cleavage fracture with a length scale - influence of material parameters and constraint. Int J Fract 2002; 118:99-118], includes a non-local stress with an associated material related length scale, and it also includes a strain measure to account for the number of nucleated cleavage initiation sites. The experiments were performed on single edge cracked bend test specimens with three different crack lengths at the temperature 85 degrees C, which is in the upper transition region for the steel in question. The ductile rupture process is modelled using tile cell model for nonlinear fracture mechanics. The original cleavage fracture model had to be modified in order to account for the substantial number of cleavage initiators being consumed by the ductile process. With this modification, the model was able to accurately capture the experimental failure probability distribution.
|
|
| 35. |
- Ljustell, Pär, et al.
(författare)
-
Variable amplitude crack growth in notched specimens
- 2005
-
Ingår i: Engineering Fracture Mechanics. - Oxford : Pergamon Press. - 0013-7944 .- 1873-7315. ; 72:18, s. 2703-2720
-
Tidskriftsartikel (refereegranskat)abstract
- Predictions of variable amplitude fatigue crack growth in notched tensile specimens at an elevated temperature and relative high loads were conducted. The predictions were based on constant amplitude fatigue data and mean crack growth rates were calculated. Crack closure levels were calculated by comparison of crack closure free experimental data obtained with the so called constant K1(max)-method and nominal data. Also, numerical simulations of the closure level throughout the specimens were performed. Although experimental data showed rather large a scatter it was concluded that variable amplitude crack growth rates can be predicted with reasonable agreement using constant amplitude fatigue data. Also, crack growth rates cannot be predicted by LEFM in the inelastic notch affected zone, even if absence of crack closure is assumed.
|
|
| 36. |
- Lundmark, Peter, et al.
(författare)
-
Damage evolution and characterisation of crack types in CF/EP laminates loaded at low temperatures
- 2008
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 75:9, s. 2631-2641
-
Tidskriftsartikel (refereegranskat)abstract
- Tensile testing of CF/EP AS4/8552 cross-ply laminates at room (RT) and cryogenic (around -150 deg C) temperatures has been performed to study the effect of temperature on damage (intralaminar cracking) evolution. Microscopy studies of the specimen edges showed a significant difference in damage pattern for the two different temperatures. At the low temperature (LT), more complex crack types were obtained that could not be found in specimens tested at the RT. The effect of these crack types on the laminate tensile modulus was studied by FEM. In analytical stiffness modelling complex shape crack was replaced by an 'effective' normal (straight) crack with an 'effective' crack opening displacement (COD) that leads to the same reduction in laminate stiffness. A crack efficiency factor was introduced to characterize the significance of complex crack shapes for stiffness reduction. The reduction of tensile modulus for a laminate damaged at low temperature was measured and compared with model predictions.
|
|
| 37. |
- Mattsson, David, et al.
(författare)
-
Damage in NCF composites under tension : effect of layer stacking sequence
- 2008
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 75:9, s. 2666-2682
-
Tidskriftsartikel (refereegranskat)abstract
- Non-crimp fabric (NCF) cross-ply composites response to tensile loading is investigated showing large effect of the fabric layer stacking sequence: much larger elastic modulus reduction was observed in [0/90/0/90]S than in [90/0/90/0]S case. Since transverse cracks in 90°-bundles may give modulus decrease about 5%, the observed 40% stiffness reduction is attributed to failure and delamination of bundles oriented in the direction of the applied load. Analysis of micrographs shows extensive delaminations and 0°-bundle breaks. FE calculations showed that failure of 0°-bundles at the surface is energetically more favorable. However, the fracture resistance of surface bundles is higher due to smaller bundle waviness and the density of bundle cracks on the surface was not larger than inside. Two possible reasons for the higher stiffness reduction in the [0/90/0/90]S NCF composite were suggested: (a) If two imperfect 0°-bundle layers are separated by a 90°-bundle layer their resistance to failure is lower than when they are situated next to each other; (b) the effect of each surface 0°-bundle break on the composite stiffness is larger (due to less constraint from the surrounding material the opening of surface bundle breaks is much larger).
|
|
| 38. |
- Nilsson, Fred
(författare)
-
The 15th European Conference of Fe racture
- 2006
-
Ingår i: Engineering Fracture Mechanics. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-7944 .- 1873-7315. ; 73:2, s. 159-159
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 39. |
- Salomonsson, Kent, et al.
(författare)
-
Influence of root curvature on the fracture energy of adhesive layers
- 2009
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 76:13, s. 2025-2038
-
Tidskriftsartikel (refereegranskat)abstract
- Previously performed experiments to study the mode I behavior of an adhesive layer revealed an apparent increase in the fracture toughness when the adherends deformed plastically. Attempts to simulate the experiments are made; both with elastically and plastically deforming adherends. Thus, effects of the size of the process zone and the deformation of the adherends are revealed. The adhesive layer is modeled using finite elements with different approaches; cohesive elements and representative volume elements. The adherends are modeled with solid elements. With a long process zone, all models give good results as compared to the experiments. However, only the model with representative volume elements gives good agreement for large root curvatures and correspondingly short process zones. The results are interpreted by analyzing the deformation and mechanisms of crack propagation in the representative volume elements. It is shown that with large root curvature of the adherends, the in-plane stretching of the adhesive layer gives a substantial contribution to the fracture energy. A simple formula is derived and shown to give an accurate prediction of the effects of the root curvature. This result indicates the limits of conventional cohesive zone modeling of an adhesive layer of finite thickness.
|
|
| 40. |
- Sieurin, Henrik, et al.
(författare)
-
Fracture toughness of a welded duplex stainless steel
- 2005
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 73, s. 377-390
-
Tidskriftsartikel (refereegranskat)abstract
- The present work includes fracture toughness testing on 30 and 50 mm thick duplex stainless steel 2205 (22% Cr, 5.5% Ni, 3% Mo, 0.15% N). Base metal and submerged arc weldments (SAW) at subzero temperatures have been tested using full size three point bending. The evaluation of the results has been carried out using J-integral calculations and correlations to Charpy impact values. It is shown that the temperature dependence of the fracture toughness can be described by a transition temperature curve, the master curve. The reference temperature was evaluated to -143 and -101 degrees C for base and weld material respectively.
|
|
| 41. |
|
|
| 42. |
|
|
| 43. |
- Wall, Ola
(författare)
-
Dynamic crack propagation in large steel specimens
- 2002
-
Ingår i: Engineering Fracture Mechanics. - 1873-7315. ; 69:7, s. 835-849
-
Tidskriftsartikel (refereegranskat)abstract
- Dynamic fracture experiments on crack initiation and crack growth in single edge bend specimens are performed. The impact velocity is in the range of 14 to 50 m/s and the specimen size is 320 x 75 mm with a thickness varying from 18 to 40 mm. The experiments are recorded by high speed photography. Two different steel qualities are investigated and their constitutive characterisation are obtained from uni-axial tension tests and shear tests with strain rates in the range 10(-4) to 10(3)s(-1) and tension tests at temperatures between -196 and 600degreesC. One of the materials exhibits a transition from a ductile dimple fracture to a brittle cleavage fracture as the loading velocity increases and as the specimen thickness increases. Scanning electron microscope fractographs show that the density of plastic bridges within cleavage ligaments decreases with increasing impact velocity and with increasing specimen thickness. It is also noted that the local crack propagation direction defects from the global one in cleavage fracture areas with a high density of plastic bridges. The other material fails in a ductile mode in all the investigated cases.
|
|
| 44. |
- Wall, Ola
(författare)
-
Numerical modelling of fracture initiation in large steel specimens at impact
- 2002
-
Ingår i: Engineering Fracture Mechanics. - 1873-7315. ; 69:7, s. 851-863
-
Tidskriftsartikel (refereegranskat)abstract
- Dynamic mode I fracture initiation in impact loaded single edge bend specimens with a quarter notch is investigated by numerical modelling and the results are compared with sets of experimental data from two different steel qualities. The finite element analysis include 2D (two-dimensional) plane strain, 2D plane stress and 3D models. No crack growth is included in the calculations. The impact velocities are approximately 15, 30 and 45 m/s and the specimen size is 320 x 75 mm. 2 with a thickness of 20 or 40 mm. Some specimens have side grooves. Details of the deflection of the specimens are accurately reproduced prior to crack initiation both by the 2D plane strain model and by the 3D model. The experiments were performed in the ductile to brittle transition region. It is assumed that cleavage fracture initiation can be predicted by the Ritchie-Knott-Rice (RKR) model, i.e. cleavage fracture initiates when the opening stress exceeds the macroscopic cleavage stress over a fixed, critical distance. At an impact velocity of 15 m/s, fracture initiation by void nucleation and growth is observed, though the RKR-conditions is seemingly fulfilled according to the computational results. Possible limitations in the use of the RKR model are discussed.
|
|
| 45. |
- Zerbst, Uwe, et al.
(författare)
-
Introduction to the damage tolerance behaviour of railway rails – a review
- 2009
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944. ; 76:17, s. 2563-2601
-
Tidskriftsartikel (refereegranskat)abstract
- Despite substantial advantages in material development and in periodic non-destructive inspection together with periodic grinding and other measures in order to guarantee safe service, fatigue crack propagation and fracture is still in great demand as emphasised by the present special issue. Rails, as the heart of the railway system, are subjected to very high service loads and harsh environmental conditions. Since any potential rail breakage includes the risk of catastrophic derailment of vehicles, it is of paramount interest to avoid such a scenario. The aim of the present paper is to introduce the most important questions regarding crack propagation and fracture of rails. These include the loading conditions: contact forces from the wheel and thermal stresses due to restrained elongation of continuously welded rails together with residual stresses from manufacturing and welding in the field, which is discussed in Section 2. Section 3 provides an overview of crack-type rail defects and potential failure scenarios. Finally the stages of crack propagation from initiation up to final breakage are discussed.
|
|
